The present exemplary embodiments relate to printing systems and, in particular, printing devices which utilize a supply of colored inks to be communicated to a print head for document printing. More particularly, the present embodiments utilize solid ink sticks as the supply ink, which must be heated to a liquid form before being capable of communication to the print head. Such systems are commercially available under the PHASER® mark from Xerox Corporation.
The present embodiments concern the structure, control system and operation methods of the heater element for causing a phase change in the solid ink supply to a liquid form capable of fluid communication to a print head for document printing.
The basic operation of such phasing print systems comprises the melting of a solid ink stick, its communication to a reservoir for interim storage, and then a supply process from the reservoir to a print head for printing of a document. The object of the control strategy is to avoid the printing system running out of ink while trying to print, because such an event can be a catastrophic failure to the system. Prior known systems will typically supply a measuring device in the reservoir to monitor ink levels therein. When the ink drops below a certain level due to normal usage, then the ink supply control system would melt more of the solid ink supply until the reservoir would refill to the desired level. The steps of asking for more ink, turning on the melter to melt the solid ink, delivering the ink to the reservoir to a desired level and then turning the heater off is commonly referred to as an “ink melt duty cycle.” It is an operating feature of such systems that as the frequency of melt duty cycle changes, the flow rate characteristics of the heating system will correspondingly change. For higher frequency duty cycles, the melt rate goes up; for lower frequencies, the melt rate goes down.
Conventional systems used a fixed applied power supply to the heater that was predetermined to provide a desired melt rate, but since only one level of applied power was available, the actual melt rate could vary depending upon consequential ambient variant conditions or varying printing operations, i.e., a high demand of certain ink color versus a low demand of another ink color would result in different frequencies of the melt duty cycles for the different colors. Where the printing system is printing an unusually large amount of a particular color, the corresponding increase in frequency of the ink melt duty cycle similarly may have a consequence on the desired flow rate, that is, the supply ink may be heated to a higher temperature than normally expected before the start of a next duty cycle due to failure to have enough cool down times between the cycles. Additionally, it is not unusual for such printing systems to be employed in out of office environments such as in an unheated storage warehouse in a colder location to an uncooled airplane hangar in a desert location. Extreme ambient temperature conditions such as these examples can have an effect on the flow rate in a heating process where the heating element receives only a single level of applied power.
There is a need for an improved adaptive control system for the power supply for such ink melt heaters that can avoid the variances of ink melt rates resulting from consequential variant conditions. Improved precision in ink flow rate control provides consequent efficiencies in ink handling, i.e., less heat losses, smaller reservoir requirements and less heating of ink therein over shorter periods of time. The present exemplary embodiments satisfy this need as well as others to provide an adaptive power control system for ink melt heaters in phasing printing systems that can provide a substantially uniform ink melt rate. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications where the supply of power to the heating element needs to be adjusted for enhanced control of items heated by the heater element.